1. Field of the invention
The present invention relates to a communication technology in a mobile communication system including a plurality of base station apparatuses and a base station controller.
2. Description of the Related Art
LTE (Long Term Evolution) given a generic name is a high speed data communication system for mobile equipment, of which the standardization is now underway in 3GPP (3rd Generation Partnership Project). The LTE is ranked stepwise for a smooth shift to the next generation (4G) in a way that attains further evolutions of the W-CDMA (Wideband Code Division Multiple Access) system called 3G, HSDPA (High Speed Downlink Packet Access) system called 3.5G, etc.
In the mobile communication system adopting the LTE, a conventional RNC (Radio Network Controller) function is shared among an evolved NodeB (which will hereinafter be abbreviated to eNB) defined as a base station apparatus, an MME (Mobility Management Entity) defined as a base station controller in a core network system and a serving gateway (which will hereinafter be abbreviated to serving GW) (also called SAE GW), whereby the RNC device itself is deleted. This type of LTE mobile communication system gets diversified in terms of a topology among the eNB, the MME and the serving GW.
FIG. 15 is a diagram showing an example of a system architecture of the conventional LTE mobile communication system. As exemplified in FIG. 15, in the LTE mobile communication system, the same mobile communication system accommodates eNB 501 having an oriented communication area for a public network and home eNB 502 having an oriented communication area for an individual user. Namely, a considerable number of eNB 501 and home eNB 502 are connected via a IP network 500 to an MME 505 and a serving GW 506.
By the way, a communication protocol in the LTE mobile communication system is configured by a user plane (which will hereinafter be simply referred to as the U-plane) that handles transmission and reception of user data between users and a control plane (which will hereinafter be simply referred to as the C-plane) that handles control of user calls and connections in order to control the U-plane. In the LTE mobile communication system, a transport layer protocol on the C-plane involves utilizing SCTP (Stream Control Transmission Protocol), and a transport layer protocol on the U-plane involves utilizing GTP (GPRS (General Packet Radio Service) Tunneling Protocol) and UDP (User Datagram Protocol).
The SCTP enables a connection called an SCTP association to be established between end points, and plural streams of user messages to be independently forwarded within the SCTP association. The GTP involves employing a GTP tunnel, thereby transparently forwarding a data packet transmitted and received between mobile terminals (user equipment (UE)) on the mobile communication system network including the IP network 500.
FIGS. 16 and 17 are conceptual diagrams showing a topology on the C-plane and a topology on the U-plane in the conventional LTE mobile communication system. As illustrated in FIGS. 16 and 17, according to the conventional LTE mobile communication system, the eNB 501, eNB 502 and eNB 503 are each linked to the MME 505 and also connected to each other. Herein, in the interfaces employed on the application layer of the individual nodes utilizing the SCTP layer or the GTP layer, the interface connecting each node eNB to the MME is called an S1 interface (depicted by an arrowhead of a solid line in FIGS. 16 and 17), and the interface establishing the connection between the eNB is called an X2 interface (depicted by an arrowhead of a broken line in FIGS. 16 and 17). A message on the application layer, which is sent and received via this S1 interface, is notated by an S1-AP message, and a message on the application layer, which is sent and received via the X2 interface, is notated by an X2-AP message.
Further, FIGS. 16 and 17 show examples, in which two outbound streams (the SCTP streams for transmission) and two inbound streams (the SCTP streams for reception) are set up between the individual nodes on the C-plane, and a single outbound GTP tunnel (the GTP tunnel for transmission) and a single inbound GTP tunnel (the GTP tunnel for reception) are set up between the respective nodes on the U-plane.
In such a case, as illustrated in FIG. 16, in the conventional topology on the C-plane, SCTP associations 510 through 517 are established in which the four SCTP streams are set up between the MME 505 and the eNB 501, eNB 502 and eNB 503, and the four SCTP streams are set up among the eNB 501, eNB 502 and eNB 503. The four SCTP streams for the S1 interface are set up in the SCTP associations 510, 511 and 512, and the four SCTP streams for the X2 interface are set up in the SCTP associations 515, 516 and 517.
The conventional topology on the U-plane is that as illustrated in FIG. 17, inbound security associations and outbound security associations are established respectively between a serving GW 506 and the eNB 501, eNB 502 and eNB 503 and between the respective eNB 501, eNB 502 and eNB 503. The security association connotes a logic communication path established by exchanging items of information such as an encryption system and an encryption key on the basis of IPSec (Security Architecture for Internet Protocol) and IPv6.
Furthermore, one GTP tunnel is set up in each security association. To be specific, the two GTP tunnels for the S1 interface are set up in each of the GTP tunnel groups 520, 521 and 522, and the two GTP tunnels for the X2 interface are set up in each of the GTP tunnel groups 525, 526 and 527.
The LTE mobile communication system as shown in FIG. 15 is assumed to accommodate the oriented eNB 501 for the public network and home eNB 502, and hence the MME 505 and the serving GW 506 need to establish the security associations for the SCTP associations and the GTP tunnels between the considerable number of eNB.
Accordingly, there is a necessity for managing the multiplicity of SCTP associations and security associations, and consequently there arise processing loads on the MME 505 and the serving GW 506. Further, a predetermined traffic occurs for establishing these associations, and hence a traffic quantity within the mobile communication system increases.
The eNB 502 assumed to be used for an individual user and might undergo frequent power ON/OFF operations, and therefore these operations lead to frequent occurrence of high-load processes such as processes of establishing and releasing the SCTP associations and an IPsec key exchange procedure.
Accordingly, if there increases the number of accommodated home eNB causing the frequent occurrence of the high-load processes, there arise the processing loads on the MME and the serving GW for controlling the nodes. Moreover, those processes entail plural flows of traffic, and hence there increases the traffic flowing across the IP network 500 that connects each eNB to the MME or the serving GW.